Magnetron



Patented July 2, 1940 UNITED STATES MAGNETRON Ernest G. Linder,Philadelphia, Pa., assignor to Radio Corporation of America, acorporation of Delaware v Applicationseptember 30, 1938, Serial No.232,489

9 Claims. 1 (01. 250-36) My invention relates to improvements inmagnetrons in which greater efficiency and improved electron control areattained by providing end plate electrodes which are divided into two ormore segments and which, in one form of my invention, are coupled to theanode electrodes.

It is an object of my invention to provide means for increasing theelectron control in a magnetron.

It is another object of my invention to provide sectionalized end plateelectrodes in a magnetron, each section of which may be energizedindependently.

It is a further object of my invention to increase the efficiency of amagnetron by properly relating the phase of the alternating currentvoltage on the anode electrode to the voltage on the end plate or endplate segments.

A further object of my invention is to provide a new and improved formof end plate for magnetrons. a t V A still further object of myinvention is to provide means for increasing the emciency of a magnetronoscillator.

It is a still further object of my invention to provide means forreducing the electricfield distortion which is caused by end plates in amagnetron. l

The invention will be better understood from the following descriptionwhen considered in connection with the accompanying drawing. Its

' and Figure 3 is a schematic drawing of a mag netron oscillator havingsectionalized end plates which are coupled to the anode electrodes by aresonant circuit, and Figure 3 is an end view of the end platesillustrated in Figure 3% I have illustrated my invention by means of amagnetron oscillator circuit, but myinvention is applicable to amplifierand detector circuits as Well.

End plate electrodes have been utilized in magnetron oscillators for thepurpose of creating an electron flow in the direction of the axis of thecathode, and to reduce electron bombardment on the glass container. Asusually employed a high direct current potential is applied to the endplates. The normal direct potential near the 5 cathode is low in theabsence of end plates. The end plates, however, introduce a high directcurrent potential in the region of the cathode, Which distorts, thenormal electric field within the tube, and causes the electron paths tobe nonuniform. 10 That is, electrons which are emitted near the ends ofthe cathode are attracted directly to the end plates, and thus do nothave a chance to rotate about the cathode. Such electrons do not assistin the operation of the tube and therefore reduce its efficiency.

, I-have found that greater efficiency is obtained if this distortion iseliminated by sectionalizing the end plate in such a manner that highdirect current potentials may be applied in the region ,20 near theanode electrodes and lower direct current potentials may be appliedinthe region near the cathode. This is accomplished in the mannerillustrated in Figs. 1 and l, to which reference is now made. Similarreference numerals g5 refer to similar elements throughout the drawing.

Apair of anodes 5, 1, having semi-cylindrical surfaces areconcentrically arranged about a cathode 9, within an evacuated envelopeIll. The anode electrodes are connected to an antenna II by means of atransmission line l3, l5. Direct current potential is supplied to theanode electrodes by a battery I9, or the like, which is connectedthrough a radio frequency choke coil I! to the midpoint of the antenna,to one end of the cathode, and to ground. The cathode is heated by abattery 2 l. A magnetic field is supplied by a source, such as apermanent magnet, electromagnet or solenoid, which is not shown. Thefield is indicated by the arrow labeled mag- 40 netic field, andsubstantially parallel to the axis of the cathode.

It will be seen that the elements and connections so far recited arethose of the usual magnetron oscillator. According to my invention, Ihave provided at each end of the anode electrodes, and slightly spacedtherefrom, a pair of end plates comprising segments 23, 25. Each endplate is-perpendicular to the cathode axis, and consists of an outerannular segment 23, and an inner circular segment 25. The outer segments22, 23 are both connected to a high voltage tap on the battery l9, andthe inner segments 25, 25 are likewise connected to the battery It, butpreferably at a lower potential.

I have also found that the usual end plate, and. in fact the end platestructure illustrated in Fig. 1 interferes with the alternating currentfield in the region of the anode electrodes. This is because the endplates are usually at ground potential with respect to radio frequency,or at least at some indeterminate potential which is the inherent resultof the inclusion of a finite length of conductor between the end plateand the battery. I have found that the performance of a magnetronoscillator can be further improved by causing the end plate to assume analternating potential.

One method of accomplishing this further improvement in accordance withmy invention is illustrated in Figs. 2 and 2 to which reference is nowmade. Fig. 2 differs from Fig. 1 only with respect to the end plateswhich are now not only sectionalized as in Fig. 1 but the outer annularsegment 21 is also divided along a line through its diameter, thuspermitting the upper and lower half to assume the instantaneous highfrequency potential of the respective adjacent anode section. Each outersemi-annular segment Zl' is coupled to the adjacent anode by thecapacity between the segment and flanges 29 which extend radially fromeach end of the anode segments 5 and 9. Direct current potential isapplied to the outer end plate segments 21 through radio frequencychokes 3|. The inner circular end plate segment 33 is connected directlyto a suitable tap on battery l9, as before. In order to permit closecoupling between the outer end plate segments and the anode sections,the cathode 9 is brought out through a centrally located hole in theinner end plate.

As a result of the foregoing arrangement, each end plate segment followsthe potential fluctuations of the anode section to which it is adjacent.This prevents the distortion of the high frequency field. Simultaneouslythe steady electric field near the end plates, due to the steady anodepotential, is not distorted in'the cathode region, as the end platedirect current potential is much less near the cathode than in theregion near the anode.

I have discovered, further, that still more efficient oscillations areobtained if the phase of the alternating potential on the end platesegments is displaced somewhat with respect to the potential of therespective adjacent anode sections. In accordance with one embodiment ofmy invention, this is accomplished by coupling each end plate segment toits adjacent anode by a tuned circuit. Referring to Figs. 3 and 3 a pairof semi-circular end plates 35, 31 are utilized at each end of the usualsplit anode sections 5, l of the magnetron. To simplify theillustration, sectionalizing fordirect current potential control has notbeen shown in Figs. 3 and 3*, but this feature may be added in themanner shown in Figs. 2 and 2 The tuned circuits 39 couple respectiveend plate segments to the nearest end of the adjacent anode section 5 orT. The tuned circuits have been illustrated as parallel line circuits,but

It has been found also that magnetrons of the usual type utilizingcircular end plates are improved when the end plate is coupled to theanode by a tuned circuit in the manner described.

Where magnetrons are used having anodes which are split into foursections, the end plates would, of course, be divided into four equalsections.

I have thus described an improved magnetron oscillator which utilizessectionalized end plates to reduce the field distortion within the tube.I have also described several ways of connecting such end plates to theanode electrodes in order to obtain maximum efiiciency.

I claim:

1. In a device of the character described, a magnetron comprising ananode, a cathode, and sectionalized end plates, respective sections ofwhich are adapted to be operated at different potentials with respect tosaid cathode, and means for producing a magnetic field.

2. In a device of the character described, a magnetron comprising ananode, a cathode, and sectionalized end plates, means for producing amagnetic field, and means, for applying different potentials betweensaid cathode and the sections of said end plates, for reducing thedistortion of the electric field within said magnetron.

3. In a device of the character described, a magnetron comprising ananode, a cathode, and sectionalized end plate electrodes, means forproducing a magnetic field, and means for applying different potentialsbetween said cathode and respective sections of said end plates, forreducing the distortion of the high frequency'alternating electric fieldwithin said magnetron.

4. In a device of the character described, a magnetron comprising acathode, a split anode and sectionalized end plate electrodes, means forproducing a magnetic field, and means for maintaining diiferent sectionsof said end plate electrodes at different direct current potentials withrespect to said cathode.

5. In a device of the character described, a magnetron comprising acathode, a concentric split anode, and sectionalized end plateelectrodes, means for producing a magnetic field, means for maintaininga section of said sectionalized end plate at the alternating currentpotential of an adjacent anode section, and means for maintaining saidsection at a different direct current potential with respect to saidcathode from that of said adjacent anode and from that of the othersection of said sectionalized end plate.

6. In a device of the character described, a

magnetron comprising a cathode, a concentric split anode, andsectionalized end plate electrodes, said end plate electrodes comprisingan outer annular section and an inner concentric circular section, meansfor producinga magnetic field whose lines of force are parallel to saidcathode, and means for independently applyingdirect current potentialsbetween cathode and the inner and outer sections of said end plateelectrodes.

'7. In a device of the character described, a

magnetron comprising a cathode, a split anode,

and two sectionalized end plate electrodes, each of said sectionalizedend plates comprising semicircular elements arranged in a planeperpendicular to said cathode and adjacent to the ends of I said splitanode electrodes, means for applying direct current potentials betweencathode and said anode and between cathode and said end plateelectrodes, and means for coupling said end plate sections to adjacentanode sections.

8. In a device of the character described, a magnetron oscillatorcomprising a cathode, a split anode and two sectionalized end plateelectrodes, each of said end plate electrodes comprising two equalsemi-annular sections enclosing aniinner current potentials between saidcathode and said circular end plate sections and said anode sections,and means for producing a magnetic field. 9. A magnetron comprisingcathode, anode and end plate electrodes, means for producing a magneticfield parallel to and surrounding said cathode, an oscillatory circuitconnected to said anode for producing an oscillatory voltage on saidanode and coupling means connected between said anode and end plateelectrodes for applying said oscillatory voltage to said end plateelectrodes, said coupling means providing a predetermined phasalrelationship between the voltage on said anode electrode and thatapplied to 10 said end plate electrodes.

ERNEST G. LINDER.

